Download 4 Cells ? the units of life Principles of Biology BIOL 1543 Greig Roberts, DDS Office: SCEN 417 E-Mail: firstname.lastname@example.org 0 The Art of Looking at Cells Early scientists who observed cells made detailed sketches of what they saw These early sketches revealed an important relationship between art and biology, the most visual of the sciences Life began on a young Earth Planet Earth formed some 4.6 billion years ago Fossilized prokaryotes called stromatolites date back 3.5 billion years The early atmosphere probably contained H2O, CO, CO2, N2, and some CH4 Volcanic activity, lightning, and UV radiation were intense How did life form? Simulations of Earth?s early conditions have produced amino acids, sugars, lipids, and the nitrogenous bases found in DNA and RNA. Cooled water containing organic molecules Cold water Condenser Sample for chemical analysis H2O ?Sea? Water vapor ?Atmosphere? Electrode CH4 NH3 H2 Other critical steps Organic polymers such as proteins and nucleic acids may have formed on hot rocks or clay. The first genetic material and enzymes may both have been RNA. G A G G C G G G C C C A A A A U U U U G C U A U G C A U U C G G U U U G C A U A U G C A 1 2 Formation of short RNA polymers: simple ?genes? Assembly of a complementary RNA chain, the first step in replication of the original ?gene? Monomers Additional critical steps Membranes may have separated various aggregates of self-replicating molecules (RNA and polypeptides), which could then be acted on by natural selection. LM 650? Membrane Polypeptide RNA PROKARYOTES Prokaryotes appeared on Earth billions of years ago. They are the oldest life-forms and remain the most numerous and widespread organisms. The prokaryote domains (Archaea and Bacteria) are distinguished mainly by genetic differences. Colorized SEM 650 ? The two kinds of cells, prokaryotic and eukaryotic Prokaryotic cell Nucleoid region Nucleus Eukaryotic cell Organelles Prokaryotic cells are small, relatively simple cells that do not have a membrane-bound nucleus Size of a cell A small cell has a greater ratio of surface area to volume than a large cell of the same shape. 30 ?m 10 ?m 30 ?m 10 ?m Surface area of one large cube ? 5,400 ?m2 Total surface area of 27 small cubes ? 16,200 ?m2 PROTISTS - the early Eukaryotes The eukaryotic cell probably originated as a community of prokaryotes Eukaryotic cells evolved from prokaryotic cells more than 2 billion years ago The nucleus and endomembrane system probably evolved from infoldings of the plasma membrane Mitochondria and chloroplasts probably evolved from aerobic and photosynthetic endosymbionts, respectively A model of the origin of eukaryotes Cytoplasm Ancestral prokaryote Plasma membrane Mitochondrion Chloroplast Photosynthetic eukaryotic cell Photosynthetic prokaryote Aerobic heterotrophic prokaryote Ancestral host cell Endosymbiosis Mitochondrion Endoplasmic reticulum Nucleus Nuclear envelope Cell with nucleus and endomembrane system Membrane infolding Eukaryotic cells are partitioned into functional compartments All other forms of life are composed of more complex eukaryotic cells distinguished by the presence of a true nucleus. Membranes form the boundaries of many eukaryotic cells, compartmentalizing the interior of the cell and facilitating a variety of metabolic activities. An animal cell contains various membranous organelles Nucleus Smooth endoplasmic reticulum Rough endoplasmic reticulum Ribosomes Golgi apparatus Plasma membrane Mitochondrion Lysosome Plant cells Plant cells have structures that an animal cell lacks, such as chloroplasts and a rigid cell wall. Central vacuole Chloroplast Cell wall Golgi apparatus Nucleus Smooth endoplasmic reticulum Mitochondrion Plasma membrane Rough endoplasmic reticulum The Endomembrane System The endomembrane system is a collection of membranous organelles that manufactures and distributes cell products The largest organelle is usually the nucleus, which is separated from the cytoplasm by the nuclear envelope The nucleus is the cellular control center, containing the cell?s DNA, which directs cellular activities The Endomembrane System Nucleus Chromatin Nucleolus Pore Ribosomes Rough endoplasmic reticulum Two membranes of nuclear envelope The Smooth Endoplasmic reticulum Smooth endoplasmic reticulum has a variety of functions Smooth endoplasmic reticulum, or smooth ER Synthesizes lipids Processes toxins and drugs in liver cells Stores and releases calcium ions in muscle cells Smooth ER Rough ER Nuclear envelope Rough endoplasmic reticulum makes membrane and proteins The rough ER manufactures membranes Ribosomes on the surface of the rough ER produce proteins that are secreted, inserted into membranes, or transported in vesicles to other organelles The Rough ER The Rough ER Protein inside transport vesicle 4 Transport vesicle buds off 3 Rough ER Folded protein 2 Polypeptide Ribosome 1 Stacks of membranous sacs receive and modify ER products, then ship them to other organelles or the cell surface. Transport vesicle from the Golgi ?Shipping? side of Golgi apparatus Golgi apparatus ?Receiving? side of Golgi apparatus Transport vesicle from ER New vesicle forming The Golgi apparatus finishes, sorts, & ships cell products Lysosomes are digestive compartments within a cell Lysosomes are sacs of enzymes that function in digestion within a cell Lysosomes in white blood cells destroy bacteria that have been ingested They also recycle damaged organelles Abnormal lysosomes can cause fatal diseases Vacuoles Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole, which has lysosomal and storage functions Chloroplast Central vacuole Nucleus The endomembrane system Nucleus Smooth ER Nuclear envelope Golgi apparatus Lysosome Vacuole Plasma membrane Rough ER Transport vesicle from ER to Golgi Transport vesicle from Golgi to plasma membrane ENERGY-CONVERTING ORGANELLES Chloroplasts, found in plants and some protists, convert solar energy to chemical energy in sugars. Chloroplast Stroma Inner and outer membranes Granum Mitochondria carry out cellular respiration, which uses the chemical energy in food to make ATP for cellular work. Inner membrane Outer membrane Cell surfaces protect, support, and join cells Plant cells are supported by rigid cell walls made largely of cellulose. Plasmodesmata are the connecting channels. In animals, gap junctions allow substances to flow from cell to cell. Plasma membrane Cytoplasm Plasmodesmata Vacuole Layers of one plant cell wall Walls of two adjacent plant cells
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